SELF-CONSISTENT-FIELD CALCULATION OF PAULI REPULSION AND DISPERSION CONTRIBUTIONS TO THE SOLVATION FREE-ENERGY IN THE POLARIZABLE CONTINUUMMODEL

By using the theory of intermolecular forces, two new expressions for Pauli repulsion and dispersion contributions to the solvation free ene rgy are derived. These expressions contain explicitly the solute elect ron density and, therefore, can be used directly in the SCF calculatio n of the solute wave function within the polarizable continuum model ( PCM). The final expressions are very simple and include also some intr insic solvent properties which are, for repulsion, the density, the mo lecular weight, the number of valence electrons, and for dispersion, t he refractive index and the ionization potential. This new approach do es not depend on any given intermolecular potential and it can be adap ted to any choice of basis set. For small-size basis sets, even minima l, the dispersion contribution is obtained in two steps and includes t he effect of adding diffuse and polarization functions, not used in th e wave function itself. This method has been implemented in our HONDO package, in a version which includes the cavitation contribution, dete rmined by the Pierotti-Claverie method, and the polarization contribut ion determined by the Miertus-Scrocco-Tomasi method. Some preliminary results on solutes containing C, H, O, and N are presented for solvati on in water, n-hexane, and l-octanol. The quality of these results, gi ven the simplicity of the PCM, is acceptable and of great interest for future developments.